A high carbohydrate (CHO) high fiber diet and exercise have been promoted by health professionals as an important way to prevent NIDDM or to help prevent the vast array of symptoms that result from the disease. We have demonstrated that regularly performed aerobic exercise improved glucose tolerance (OGTT), insulin stimulated glucose uptake and skeletal muscle GLUT-4 levels in older, glucose intolerant men and women. However, when combined with a eucaloric, high CHO, high fiber diet (60 percent CHO, 20 percent fat, 20 percent protein, 25 g fiber/1000 kcal) there were no exercise induced improvements in OGTT, meal tolerance, or insulin stimulated glucose uptake. The high CHO diet was also associated with a significant drop in HDL cholesterol and an increase in circulating triglyceride levels. This was a carefully controlled metabolic study in which subjects were not permitted to lose body weight. A subsequent investigation demonstrated that when older men and women consume a similar high CHO diet ad libitum (with no attempt at energy restriction), they experience significant weight loss. Using a group of older men and women (120 through 150 percent of ideal BMI, age 65 to 80 years), we propose to examine the influence of an ad libitum high CHO diet alone or in conjunction with an aerobic exercise program on body composition, insulin action, and muscle metabolism. We propose to test the hypothesis that when subjects consume a high CHO, high fiber diet ad libitum, they will lose weight and demonstrate increases in glucose tolerance and insulin stimulated glucose uptake. We will also examine the effects of a hypocaloric (-500 kcal/d) high CHO diet alone and in conjunction with an aerobic exercise to produce an energy deficit. Specifically, we will examine body composition, insulin stimulated glucose disposal (during a euglycemic, hyperinsulinemic clamp), components of energy metabolism, muscle strength and power, maximal aerobic capacity and muscle metabolism (fiber type and size, glycogen synthase, glycogen content, GLUT 4 mRNA) before and after 3 months of weight loss. This study will be the first to examine metabolic effects of an ad libitum and a hypocaloric high CHO diet (with or without exercise) in the elderly. The proposed studies will have important implications for the treatment of obesity and its vast array of complications that are often seen in older men and women.